When drafting slivers in drafting devices, the clamping action of the roller pairs plays a decisive part for the transmission of the drafting forces onto the fiber bundle. The roller pairs of a drafting device therefore consist of a lower, channeled steel roller, the so-called bottom roller, and of an upper roller, the so-called top roller, that is pressed by a loading apparatus onto the bottom roller. This top roller generally has an elastic coating so that no clamping line is produced but rather a clamping surface by the deformation of the elastic coating, which surface brings about a distinctly better retention of the fibers. A good clamping action is exerted on the fiber bundle without damaging the fibers. Experience has shown that soft roller coatings therefore yield better drafting results since the softer the coating is, the larger the clamping action is. However, the soft roller coatings have the disadvantage that they wear very rapidly and must be reground. This changes the geometry of the drafting cylinder and therewith also the properties of the coating, which for its part has a disadvantageous effect on the drafting conditions and thus on the yarn quality. Moreover, the grinding of the roller is an expensive measure.
In order to unite a high degree of softness of the roller coating with high wear resistance and thus create optimal drafting conditions for a long time of use, DE 102 60 025.2 (that is not a prior publication) suggests surrounding a top roller with a soft coating with an apron with a high wear resistance. This separate apron has the advantage that it can be readily replaced in the case of wear or damage. A replacement by an apron with a different hardness, a different method, or some other different type or quality, is readily possible.
It is obvious that this solution is advantageous, in particular on the front roller pair of a drafting device in which the rollers run especially rapidly and have the greatest influence on a reliable drafting.
The surrounding of the top front rollers of drafting devices with aprons is known (DE 816 069; DE-GM R7). The explained purpose of these rather long aprons is to prevent the formation of windings around the top rollers of the front roller pair. These aprons are associated with tensioning devices that keep them under tractive tension and thus keep them tight.
The aprons are conducted on these tensioning devices via stationary deflection members. It turned out that drive energy is consumed by the aprons being drawn over these deflection members, the aprons experience a braking that has a disadvantageous effect on the drawing process and are subject to wear.
The present invention therefore has the problem of avoiding these disadvantages.